The structure and properties of anhydrous end members of the garnet family
were investigated by quantum mechanical calculations as a function of appli
ed pressure. The results were used ro analyze the compression mechanism of
the garnet structure. Hydro-grossular and hydropyrope were also studied at
ambient and high pressure; the experimentally observed difference in the st
ability of the hydrogarnet substitution in grossular and pyrope is explaine
d here. In addition, the potential energy surface for magnesium in the pyro
pe structure is discussed in relation to vibrational properties and to poss
ible cation disorder in pyrope.